The levels of luteinizing hormone (LH), follicular stimulating hormone (FSH), 17-oestradiol (E2), progesterone (P), and testosterone (T) were determined for the early, midfollicular and periovulatory phase of spontaneous and clomiphene citrate (CC) induced cycles in 5 patients who responded with appearance of hostile cervical mucus (Group A) and 5 patients whose cervical mucus remained unchanged during the same treatment (Group B). The patients with hostile mucus were further investigated during a third cycle stimulated by CC and ethinyloestradiol (EE). Patients treated with CC for induction of ovulation who developed hostile cervical mucus showed higher levels of LH and T in the midfollicular phase of the menstrual cycle and significantly higher levels of T in the periovulatory period compared to patients with unchanged mucus. EE treatment induced a drop in the elevated LH and T levels and improved the cervical score. No change in E2 levels was noted. A direct effect of EE on the cervical glands together with the centrally mediated lowering of serum T are suggested to be responsible for improving the cervical mucus.